This invention pertains to a method and to an apparatus for measuring certain parameters, such as dielectric constant and flow rate, of fluid within a conduit.
While the invention has significant utility in a wide field of applications, the same is disclosed herein in connection with a medical application wherein it has been found to offer particular initial utility. More specifically, the method and apparatus of the invention are described in the setting of monitoring the intravenous supply of fluid to a patient in a hospital, or the like.
There are many instances where it is both desirable and important to be able to monitor certain characteristics of fluid which is flowing in a conduit. One setting, familiar to many people, is that where certain fluids are being introduced intravenously into a patient. In this setting, it is important for attendant medical personnel to know, for example, that there is no chemical change occurring in the prescribed fluid, as for example could occur if another non-prescribed fluid were inadvertently introduced into the system, that blood were to back up into the system, or that air bubbles have been introduced into the system. Rate of flow can also be an important matter to watch.
A general object of the present invention is to provide a highly-accurate non-perturbing method and apparatus for monitoring such fluid parameters within a conduit which forms part of the fluid-flow system.
More particularly, an object of the invention is to provide such a method and apparatus which employs a bidirectionally radiating lens which forms part of a very high-Q resonant cavity, with a defined length of conduit, which carries the fluid of interest, disposed on one side of the lens, wherein the conduit length is subjected to microwave radiation. The invention further employs a receiving electrode disposed on the opposite side of the lens, wherein voltage-amplitude signal levels are monitorible. Still another object of the invention is to provide a method and apparatus of the type generally outlined which is easily used.
The method and apparatus of the invention utilize information derived from what is referred to herein as a defined, or predetermined, length of conduit, which conduit is substantially transparent to microwave-frequency radiation. This defined length of conduit is placed in a preferred position on one side of the lens in order to maximize signal-to-noise ratio. The amplitude of voltage signals developed in the receiving electrode are, through pre-system calibration, directly readable to provide information about the dielectric constant of fluid flowing in the system, and also to provide fluid-flow-rate information. Two different kinds of receiving electrodes are disclosed herein, each of which promotes a slightly different way of deriving flow-rate information. The apparatus and method are non-perturbing in the sense that no transducer is introduced directly into the fluid stream.
Those skilled in the art will recognize that information about the dielectric constant of fluid flowing within a fluid-flow system is directly interpretable to indicate the nature, or material characteristics, of the fluid flowing in the system, given the fact that, in any particular application, the user will know, generally, the different categories of fluids which could be expected to appear in the system.
These and other objects and advantages which are attained by the invention will become more fully apparent as the description which now follows is read in conjunction with the accompanying drawings.